Based on a deep-water steel cofferdam foundation engineering, the technique combining the high pressure rotary spray pile seepage wall and bottom plate lower grouting was applied to strengthen the leakage of the deep steel cofferdam. According to the result of the first pumping after the reinforcement, from the actual effect, there was no any water seepage channel and reinforcement effect was very good. The reinforcement results show that by the high-pressure rotary jet pile, the passage outside the cofferdam effectively has been extended and the range has been separated below the cofferdam bottom plate into a relatively closed environment. It avoided the loss of the grouting slurry under the bottom plate and the grouting quality has been guaranteed. Through the cofferdam bottom plate range and the bottom plate grouting, the bottom plate was basically compacted and the original and possible bottom plate seepage channel were blocked.